This invention relates to a fluid pressure responsive electric switch apparatus, and particularly a "pneumatic" electric switch unit, which is adapted to sub-miniature construction.
Pressure responsive switches are widely used in various industrial as well as consumer product applications. Generally, in the prior art, a movable wall, such as flexible diaphragm unit, is incorporated in a pressure chamber unit coupled to actuate a switch mechanism secured to switch chamber. For example, U.S. Pat. No. 5,001,317 which issued on Mar. 19, 1991 to Louis D. Atkinson et al and is assigned to a common assignee with this application, discloses a highly versatile and practical pneumatic switch structure. As more fully disclosed therein, the switch structure includes a switch chamber within which a snap action switch unit is mounted. An actuator projects through the snap action switch unit and is coupled directly thereto for moving the switch with respect to the opposite ends of the switch housing. At least one end includes a diaphragm enclosure defining a pressure chamber. The opposite end is provided with a similar diaphragm pressure chamber to produce a deferential switch, with a spring loaded reset or manual reset. Although such a switch structure provides a highly satisfactory functional responsive, its application has been primarily directed to installations which permit a pneumatic-to-electric switch structure of a significant physical size construction.
The development of miniaturized and compact circuit systems has created a continuous demand for ever smaller pressure responsive switches, and particularly pneumatically operated electric switches. Thus, certain applications often include size specifications for a pneumatic-to-electric switch having a maximum width of about one-half inch and a maximum length of about one inch. Further, the switch structure should provide for adjustment of the pressure set point and/or also permit factory setting of the set point. The small pressure responsive switches should preferably operate for either or both positive pressures and vacuum pressures ranges. Thus, in a typical application which has been considered, the switch structure must operate under a three ampere load and operate with a working positive pressure range of zero to 100 PSI (pounds per square inch) and a vacuum pressure range of zero to 30 inches (Hg) (of mercury). The device often must be chemically resistant and operate with a stable functioning at temperatures of 250.degree. F. The structure must be as small as possible physically while being repairable and highly cost effective both in original manufacture and maintenance.